Not Applicable.
This invention relates to the use of electro-mechanical and electro-acoustic transducers for the production and reception of under water sound. There is significant interested in developing directional underwater acoustic transducers for several underwater application including acoustic modem underwater communication networks, point-to-point underwater communications and in improved sonar applications. Transducers that have directionality, conserve electrical power, improved signal-to-noise ration, greater signal bandwidth, improved maximum depth operation, and/or compact size are highly desirable for both commercial and naval applications. Directional transducers permit the acoustic energy to be directed where the signal is needed and eventually will be received thereby saving limited electrical power and increasing covertness. Directionality of the radiation pattern will also result in higher signal-to-noise ratio when the transducer is used as a receiver and will enhance overall performance when the device is part of a communication or sonar network. Since the signal-to-noise ratio will be increased and the acoustic signals are not radiated in all directions, a directional transducer will reduce the probability of intercept. This is due to the simple result that acoustic radiation will be directed at a known location versus in all directions.
There are existing transducers that produce directional radiation. When the acoustic transducer dimension or acoustic aperture is sufficiently large compared to an acoustic wavelength, the radiation is directional. Arrays of transducers also produce directional acoustic radiation. However, it is desirable to use compact or small sources that produce directional radiation. Several such sources exist including electrodynamic piston sources, longitudinal vibrators (vibrating rods) and tonpilz transducers. These transducers are well established and their advantages and disadvantages are well known to those in the field.
Accordingly, it is an object of the present invention to provide and improved electro-acoustic transduction apparatus with directional radiation and reception properties.
Another object of the present invention is to combine the use of cylindrical ring electro-mechanical transducers with conforming acoustic baffles to enhance directionality and improve signal-to-noise.
Another object of the present invention is to increase acoustic bandwidth by using multi vibration modes of the subject ring electro-mechanical transducer in conjunction with the conformal acoustic baffle.
Another object of the present invention is to increase produce nearly constant beamwidth directivity radiation patterns in the fullest extent possible.
Another object of the present invention is to combine a plurality of baffled ring transducers in practical array geometry and to achieve transducer self baffled operation.
Still another object of the present invention is to use a plurality of baffled rings of different resonant frequencies as may be accomplished with different materials or different size rings but wired electrically together in series or parallel to achieve a directional acousto-mechanical transducer with improved frequency bandwidth.
Still another object of the present invention is to use a plurality of baffled transducer rings, separated by passive spacers to achieve a larger aperture with less active transduction material but wired electrically together in series or parallel to achieve a directional acousto-mechanical transducer with improved directivity in the axial direction.
Still another object of the present invention is to use a plurality of baffled transducer rings, separated by spacers which may belong to the active radiation parts of a separate transducer to achieve a compact nested or interlaced array and allow the element to element spacing to be closer than would otherwise be possible, a characteristic important in the design and operation of arrays of said transducers.
Still another object of the present invention is to use a plurality of baffled transducer rings, each having electrodes divided in such a way that electro-mechanical excitation of the zeroth mode of azimuthal ring vibration and first mode of azimuthal vibration, or combination of these modes of vibration may be realized to achieve multiband and broadband operation features.
Still another object of the present invention is to use a plurality of baffled transducer rings, where by the circumferential acoustic baffle is extended in a tangential manner to achieve further modification of the directivity pattern of the electro-acoustic transducer and further where said baffle extensions may be separate operational transducers.
Still another object of the present invention is to use a plurality of baffled transducers in an array configuration, arranged in a closely packed and equally spaced circumferential array of nominal cylindrical array geometry whereby individual transduction elements may be energized to achieve individual directive radiation patterns, and further where the directivity pattern of each transducer is so designed to cover a particular part or angular sector of the total 360 degree azimuthal coverage, and further whereby separately all of the transducers may be energized simultaneously to achieve a near omunidirectional (constant) radiation beam pattern. Several of such compact cylindrical arrays may and have been fabricated consisting of 3, 4, 5, and 6 baffled transducer separated by 120, 90, 72, and 60 degrees respectively.
To accomplish the foregoing and other objects, features and advantages of the subject invention, there is now described herein an improved directional underwater transducer primarily embodied herein as an electro-acoustic cylindrical or ring transducer in combination with a conformal acoustic baffle. The apparatus of the present invention may be used individually or with a plurality of electro-acoustic cylindrical or ring transducers together as a single electro-acoustic transducer or as an array of electro-acoustic transducers. Of particular interest in accordance with one embodiment of the subject invention is the use of electro-mechanical transducers of the piezoelectric ring type to provide a practical realization of the invention with all its advantages describe herein. The concepts of the subject invention permit fabrication and demonstration of a compact acoustic transduction device and arrays of the same.
The piezoelectric ring is baffled in such a manner with a nominal coverage of 180xc2x140 degrees so as to produce a directional radiation that is nearly frequency independent. In the transmit mode the transducer is directional in azimuth (horizontal plane when the ring axis is configured in the vertical) with a 3 dB beamwidth that may be designed to be 30 to 100 degrees depending on the amount of acoustic baffle coverage. The baffle is so designed to fasten to the passive (not electro-mechanical) parts of the transducer while preserving a defined gap whereby a fluid or compliant material may exist in order to decrease the reradiation of acoustic energy by the acoustic baffle.
In accordance with the invention there is provide an acoustic baffle that is constructed of a suitable material, and as our research has shown, which may be realized in preferred embodiments with a) lead b) lead and polyurethane, c) syntatic foam, d) closed cell air filled foam, e) steel or other metals, f) laminate structures of composite materials, g) a thin air or air-bubble layer, h) compliant synthetic or natural rubber, or i) neighboring transducers of the piezoelectric type whereby careful attention is paid to the manner in which the baffle is connected to the electro-acoustic transducer.